Fire Technology

, Volume 49, Issue 2, pp 435–449 | Cite as

Theoretical and Experimental Study of Critical Velocity for Smoke Control in a Tunnel Cross-Passage

  • Ying Zhen Li
  • Bo Lei
  • Haukur IngasonEmail author


Theoretical analyses and model-scale experiments have been conducted to investigate the critical velocity in a tunnel cross-passage which is defined as the minimum ventilation velocity through the fireproof door to prevent smoke from flowing into a cross-passage. The effect of the fireproof door geometry, heat release rate, ventilation velocity and fire source location were taken into account. The critical velocity in a tunnel cross-passage varies approximately as 3/2 power of the fireproof door height, as one-third power of the heat release rate and as exponential law of the ventilation velocity, almost independent of the fireproof door width. The critical Froude Number mainly ranges from 5 to 10 and consequently as it is not a constant value it is not very suitable to predict the critical velocity in a tunnel cross-passage. A dimensionless correlation that can correlate well with the experimental data was proposed.


Tunnel fire Cross-passage Smoke control Critical velocity 



Area (m2)


Coefficient defined in Equation 14


Heat capacity of air (kJ/kg K)


Critical Froude Number


Gravitational acceleration (m/s2)


Height (m)


Length (m)


Mass flow rate (kg/s)


Total heat release rate (kW)


Convective heat release rate (kW)


Temperature (K)


Ventilation velocity (m/s)


Critical velocity in a tunnel cross-passage (m/s)

Greek symbols


Density (kg/s)

Sup and Subscripts


Cross-section no


Cross-section no


Cross-section no


Fireproof door in a cross-passage


Smoke flow


Full scale




Small scale







This work was sponsored by the ministry of railway of the People’s Republic of China which is gratefully acknowledged. The authors would also like to thank adjunct Prof. Zhihao Xu and adjunct Prof. Zhihui Deng for their help in these experiments. Acknowledgement to SP Tunnel and Underground Safety Centre for the support to the project.


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Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  1. 1.Department of HVAC EngineeringSchool of Mechanical Engineering, Southwest Jiaotong UniversityChengduPeople’s Republic of China
  2. 2.Fire TechnologySP Technical Research Institute of SwedenBoråsSweden

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